The isolation and analysis of nucleic acids from various biological sources is a commonly performed procedure in genetic and recombinant DNA research. As the primary genetic elements, nucleic acids will exist in various forms depending on the biological source. In the case of bacteriophages and viruses, which contain single- or double-stranded DNA or RNA, purification of nucleic acids require that the intact bacteriophage or virus particles can be recovered from the cell culture media prior to performing the nucleic acid purification steps. The procedures and chemistries commonly employed for recovering bacteriophage or viral particles prior to isolation of nucleic acids are described in detail in T. Maniatis et al.: Molecular Cloning--A Laboratory Manual, Cold Spring Harbor (1989).
In standard manual bacteriophage nucleic acid preparations the cells are separated from the bacteriophage particles by differential centrifugation. The cell-free media is transferred to a separate vessel and a precipitating agent of polyethylene glycol/sodium chloride is added to the media and mixed. The resulting solution is incubated at reduced temperature, typically 4 degrees C., for one hour or more. To insure efficient recovery of DNA, long incubations, from several hours to over night, at reduced temperatures with polyethylene glycol, are emphasized. To insure recovery of high quality DNA, incubation in the presence of protein digesting enzymes is also emphasized. Samples are then centrifuged at high speed at 4 degrees C. to recover the bacteriophage/polyethylene glycol/sodium chloride complexes. The media is aspirated and discarded, leaving the bacteriophage pellet behind. The bacteriophage are resuspended in digestion buffer and treated with protein digesting enzymes for several hours at elevated temperatures. Following this digestion, the sample is extracted repeatedly with phenol and chloroform to remove contaminating material. Nucleic acids in the resulting solution are mixed with ethanol and centrifuged to concentrate the nucleic acids. The nucleic acid pellet is washed, dried briefly and resuspended in a small volume of buffer.
In both automatic and manual DNA separation techniques, these extensive manipulations are time consuming and inefficient, making nucleic acid purification an expensive procedure.